1. Field of the Invention
The present invention relates generally to an apparatus, system and/or method for bit interleaving and/or bit de-interleaving. For example, certain embodiments of the present invention provide an apparatus, system and/or method for bit interleaving physical layer (L1) signalling for existing and future generation digital broadcasting systems, for example systems developed by the Digital Video Broadcasting (DVB) Project and/or the Advanced Television Systems Committee (ATSC).
2. Description of the Related Art
Digital broadcasting techniques allow various types of digital content, for example video and audio data, to be distributed to end users. A number of standards have been developed for this purpose, including a family of standards developed by the ATSC organization, including standards ATSC 1.0 and ATSC 2.0. The ATSC Digital Television (DTV) Standard, described in various documents, including A/52 and A/53, available at http://www.atsc.org/, have been adopted for use in terrestrial broadcasting by various countries, including the United States, Canada and South Korea.
Recently, ATSC has begun developing a new standard, known as ATSC 3.0, for a delivery method of real-time and non-real-time television content and data to fixed and mobile devices. As part of this development, ATSC has published a Call for Proposals (CFP) document (TG3-S2 Doc. #023r20, “Call for Proposals For ATSC-3.0 PHYSICAL LAYER, A Terrestrial Broadcast Standard”, ATSC Technology Group 3 (ATSC 3.0), 26 March 2013), in which a stated goal is to identify technologies that could be combined to create a new physical layer of an ATSC 3.0 Standard. It is envisaged that the ATSC 3.0 system will be designed with a layered architecture and a generalized layering model for ATSC 3.0 has been proposed. The scope of the aforementioned CFP is limited to the base layer of this model, the ATSC 3.0 Physical Layer, which corresponds to Layers 1 and 2 of the ISO/IEC 7498-1 model.
It is intended that ATSC 3.0 will not require backward compatibility with existing broadcasting systems, including ATSC 1.0 and ATSC 2.0. However, the CFP states that, wherever practicable, the standard shall utilize and reference existing standards that are found to be effective solutions to meet the requirements.
Other existing standards developed for broadcasting digital content include a family of open standards developed and maintained by the Digital Video Broadcasting (DVB) Project and published by the European Telecommunications Standards Institute (ETSI). One such standard is DVB-T2, which is described in various documents, including ETSI EN 302 755 V1.3.1, (“Digital Video Broadcasting (DVB); Frame structure channel coding and modulation for a second generation digital terrestrial television broadcasting system (DVB-T2)”), and Technical Specification ETSI TS 102 831 V1.2.1 (“Digital Video Broadcasting (DVB); Implementation guidelines for a second generation digital terrestrial television broadcasting system (DVB-T2)”).
In DVB-T2, data is transmitted in a frame structure, as illustrated in FIG. 1. At the top level, the frame structure 100 consists of super-frames 101a-c, which are divided into a number of T2-frames 103a-d. Each T2-frame 103a-d is sub-divided into OFDM symbols (sometimes referred to as cells), including a number of preamble symbols 105, 107a-c followed by a number of data symbols 109a-e. In a T2-frame 103a-d, the preamble symbols 105, 107a-c comprise a single P1 preamble symbol 105, followed by one or more P2 preamble symbols 107a-c. 
The P1 symbol 105, located at the beginning of a T2 frame 103a-d, carries 7 bits for signalling, including Si signalling used to identify the format of the P2 symbols 107a-c and S2 signalling used to signal certain basic transmission parameters. The P2 symbols 107a-c, immediately following the P1 symbol 105, are used for fine frequency and timing synchronisation and channel estimation. The P2 symbols 107a-c carry L1 signalling information, and may also carry data. The L1 signalling is divided into L1-pre signalling and L1-post signalling. The L1-pre signalling includes basic information about the T2 frame structure 100, and enables the reception and decoding of the L1-post signalling. The L1-post signalling provides sufficient information for the receiver to decode Physical Layer Pipes (PLPs) within the T2-frames 103a-d, which carry data.
A bit stream (e.g. signalling or data) typically undergoes various types of processing and encoding before the bits are mapped to symbols (cells). Bit streams carrying different types of information (e.g. L1-pre signalling, L1-post signalling and data) are typically processed differently.
FIG. 2 illustrates one example of a Bit Interleaved Coding and Modulation (BICM) chain at the transmitter side for processing a bit stream carrying L1-post signalling. The BICM chain 200 comprises a segmenter 201 for segmenting the bit stream into blocks of size Ksig, a scrambler 203 for scrambling (i.e. permuting) the bits within each block output from the segmenter 201, and a zero padder 205 for padding each block output from the scrambler 203 with zeros to obtain a padded block of size Kbch (e.g. Kbch=7032).
The BICM chain 200 further comprises a BCH encoder 207 for BCH encoding each block output from the zero padder 205 to obtain a BCH encoded block of size Nbch, also denoted Kldcp (e.g. Nbch=Kldpc=7200), and an LDPC encoder 209 for LDPC encoding each block output from the BCH encoder 207 to obtain an LDPC encoded block of size Nldpc (e.g. Nidcp=16200).
The BICM chain 200 further comprises a parity interleaver 211 for interleaving the LDPC parity bits of each block output from the LDPC encoder 209, and a puncturer 213 for puncturing Npunc of the LDPC parity bits. At this point in the BICM chain 200, the zero padded bits are also removed, resulting in blocks of size Npost.
The BICM chain 200 further comprises a bit interleaver 215 for bit interleaving each block output from the puncturer 213 to obtain bit interleaved blocks of size Npost.
Finally, the BICM chain 200 further comprises a demultiplexer 217 for demultiplexing each interleaved block output from the bit interleaver 215, and a QAM mapper 219 for mapping the demultiplexed bits output from the demultiplexer 217 to QAM symbols, which are used to generate the OFDM symbols (cells) for transmission.
A corresponding chain at the receiver side processes received symbols to recover the L1-post signalling bits.
Another possible preamble structure comprises a single symbol (e.g. OFDM symbol) having a certain length (e.g. 8K) reserved only for L1-pre and L1-post signalling. In this case, the coding and puncturing patterns used for the L1-post signalling may vary, for example depending on the length of the L1-post information (i.e. the number of L1-post information bits). The coding rate and puncturing scheme may be adapted in order to fill the entire single symbol for any length of input data.
Operation of the bit interleaver 215 shown in FIG. 2 is illustrated in FIG. 3. The bit interleaver 215 is provided in the form of a block interleaver comprising Nc columns and Npost/Nc rows. As illustrated in FIG. 3, bits are read into the bit interleaver 215 column-wise and are read out from the bit interleaver 215 row-wise to obtain the interleaved sequence. The value of Nc may vary, for example according to the modulation scheme and code rate used. For example, when using 16-QAM and a code rate of ½ then Nc=8, and when using 64-QAM and a code rate of ½ then Nc=12.
The structure illustrated in FIG. 2 has an advantage of being relatively simple. However, this structure also suffers a disadvantage of relatively poor performance in some cases. For example, a loss in performance of 3 dB can occur in some cases.
Therefore, what is desired is a method, apparatus and/or system for bit interleaving and/or bit de-interleaving in which performance can be improved while maintaining a relatively simple structure.